Evaluation of the Influence of B and Nb Microalloying on the Microstructure and Strength of 18% Ni Maraging Steels (C ₃₅₀) Using Hardness, Spherical Indentation and Tensile Tests

Microalloyed steels with very small amounts of B and/or Nb are expected to enhance their mechanical properties. In the present work, we have designed and conducted experimental assays for evaluating the merits of microalloying 18% Ni maraging steels with small amounts of B and Nb. The experiments included the synthesis of small volumes of material with the desired compositions (labeled base alloy, alloy I, and alloy II), aging heat treatments, and mechanical property evaluation using a combination of Vickers hardness, spherical indentation stress-strain protocols, and standardized tensile tests. The microstructures of the alloys were studied using SEM/EDS, EBSD, and X-ray diffraction (XRD). The results of this study have demonstrated that the microalloyed steels with B and Nb delayed the coarsening of precipitates and retained their peak aged strength over longer exposure times in the aging process. Furthermore, comparing the estimates from hardness and the spherical indentation stress-strain protocols with the standardized tensile tests indicated that the spherical indentation protocols provided highly reliable estimates of the tensile yield strengths at significantly lower cost and effort. This study has confirmed the viability of utilizing the spherical indentation stress-strain protocols for the rapid exploration of materials composition and process spaces.